RTC backup problem with SB45 on nucleo board

[xisco]

Hello,

 

I was trying to use RTC battery backup on a nucleo F446RET6.

The problem was that the battery (CR2032) connected to VBAT tries (and can't) to power all the board.

Looking to schematic diagram, I see that VBAT pin is connected to VDD thru SB45.

Removing SB45 seems that all is working fine.

Is there a reason for SB45 is there?

Thanks

[waclawek.jan]

While there is no battery (or any other separate power supply) connected to VBAT, it is recommended to have VBAT connected to VDD.

 

JW